Manufacture of tin plate



Patented Mar. 4, 1952 MANUFACTURE OF TIN PLATE John G. Donelson and Viljo W. Vaurio, Pittsburgh, Pa., assignors to United States Steel Company, a corporation of New Jersey No Drawing. Application December 9, 1947, Serial No. 790,702

3 Claims.

This invention relates to the manufacture of tin plate and more particularly to an improved method of making tin plate including the method of annealing the ferrous base metal prior to the tin coating operation.

Heretofore, corrosion resistance of tin plate was generally believed to be directly proportional to the thicknessof the tin coating. However, service results show that tin plate having the same thickness of coating may have widely different corrosion characteristics. Even in the same strip electrolytically coated under carefully controlled conditions, the edge appearance will vary and the corrosion characteristics will vary from side to side and from end to end. Applicants have discovered that the manner of annealing the ferrous base metal or strip prior to coating the same with tin has a direct bearing on the corrosion characteristics of the resultant tin plate.

It is therefore an object of the present invention to overcome the foregoing disadvantages of present day tin plate and provide a method of making tin plate which results in improved and more uniform corrosion resistance.

It is a further object of the present invention to provide a method of improving the corrosion resistance of tin plate which does not involve extra processing steps or add materially to the cost thereof.

In accordance with the teachings of our invention, tin plate stock of low metalloid steel containing between .025 to .11% carbon; .25 to .50% manganese; 015% maximum phosphorus; .05% maximum sulphur; 01% maximum silicon; .06% maximum copper and the balance substantially iron, is reduced to strip of the desired thickness by hot-rolling followed by cold-rolling. The strip after being reduced to the desired gage, may be electrolytically cleaned to remove any cooling or lubricating medium applied thereto during the cold reduction. Such metal in strip form is then coiled preparatory to annealing the same. We have discovered that the annealing, which is preferably box annealing, should be conducted at a temperature above 1200 F. and below 1350 F. and preferably at approximately 1250 F. Reducing gas, which should be substantially free of oxidizing elements, is introduced into the box or cover to prevent oxidation during the heating and cooling cycle. According to our discoveries, this annealing atmosphere should contain less than 7% combustibles and must be substantially free from carbon dioxide and water vapor. A suitable atmosphere contains between 2 and 7% hydrogen, 3.5% maximum carbon monoxide, .1%

or less carbon dioxide and .l or less water vapor with the balance being substantially nitrogen. In any event, the total of hydrogen and carbon monoxide combined should be less than 7 The water vapor content may be considered as not exceeding a dewpoint of 40 F. The preferred gas within this range contains about 2 /2 hydrogen, about 2 /2 carbon monoxide, less than .1% carbon dioxide and less than .1% Water vapor with the balance substantially nitrogen.

In the annealing cycle, approximately 24 hours is taken to heat the coils to the desired temperature which is held for about 4 hours after which the heating furnace is removed so that the charge wi l slowly cool. The cooling time is about to hours. Prior to the heating cycle, a heavy flow of the above gas through the box or cover is maintained for about 2 hours in order to sweep out all of the air before the temperature of the metal is raised sufficiently to cause any oxidation thereby. During the heating cycle the flow of gas may be at a reduced rate so that during the heating and cooling a gas pressure in the box or cover of about .4 inch of water is satisfactory.

As a result of so annealing the base stock, prior to coating, differences in corrosion resistance over the width and along the length of electrolytically coated coils, are substantially eliminated. In addition to making the corrosion resistance more uniform, service tests show that the average life of coatings produced in accordance with the teachings of the invention is raised at least 50 to for both hot-dipped and electrolytically deposited coatings.

We claim:

1. In the manufacture of tin plate, the improvement comprising box-annealing 10w metalloid ferrous tin-plate stock containing between .025 and .11% carbon, .25 to .50% manganese, 015% maximum phosphorus, .05% maximum sulphur, .01% maximum silicon, .06 maximum copper, balance substantially iron, at atemperature over 1200 F. and less than 1350 F. in a reducing atmosphere containing less than 0.1% carbon dioxide, less than 0.1% water vapor, between 2 and 7% hydrogen, between 0 and 3.5% maximum carbon monoxide, the total amounts of hydrogen and carbon monoxide not exceeding 7%, with the balance substantially nitrogen before coating the same with tin.

2. In the manufacture of tin plate, the improvement comprising box-annealing 10W metalloid ferrous tin-plate stock containing between .025 and .11% carbon, .25 to .50% manganese, 015% maximum phosphorus, .05% maximum sulphur, .01%

maximum silicon, .06% maximum copper, balance substantially iron, at a temperature of substantially 1250 F. in an atmosphere containing less than 0.1% carbon dioxide, less than 0.1% water REFERENCES CITED The following references are of record in the file of this patent:

vapor, about 2 /2% hydrogen, and 2 /2% carbon 5,

monoxide with the balance substantially nitrogen before coating the same with tin.

3. In the manufacture of tin plate, the improvement comprising box-annealing low metalloid ferrous tin-plate stock containing between .025 and .11% carbon, .25 to 50% manganese, 015% maximum phosphorus, .05% maximum sulphur, 01% maximum silicon, balance substantially iron, at a temperature over 1200 F. and less than 1350 F. in a reducing atmosphere contain- UNITED STATES PATENTS Number Name Date 131,680 Hill Sept. 24, 1872 2,040,442 Nieman May 12, 1936 2,156,607 Schon May 2, 1939 OTHER REFERENCES Metals and Alloys, July 1937, pp. 195-205 and page 202.

Metals Progress, June 1942, page 815.

Controlled Atmospheres for the Heat Treatment of Metals, by Jenkins-page 281. 

1. IN THE MANUFACTURE OF TIN PLATE, THE IMPROVEMENT COMPRISING BOX-ANNEALING LOW METALLOID FERROUS TIN-PLATE STOCK CONTAINING BETWEEN .025 AND .11% CARBON, .25 TO .50% MANGANESE, .015% MAXIMUM PHOSPHORUS, .05% MAXIMUM SULPHUR, .01% MAXIMUM SILICON, .06% MAXIMUM COPPER, BALANCE SUBSTANTIALLY IRON, AT A TEMPERATURE OVER 1200* F. AND LESS THAN 1350* F. IN A REDUCING ATMOSPHERE CONTAINING LESS THAN 0.1% CARBON DIOXIDE, LESS THAN 0.1% WATER VAPOR, BETWEEN 2 AND 7% HYDROGEN, BETWEEN 0 AND 3.5% MAXIMUM CARBON MONOXIDE, THE TOTAL AMOUNTS OF HYDROGEN AND CARBON MONOXIDE NOT EXCEEDING 7%, WITH THE BALANCE SUBSTANTIALLY NITROGEN BEFORE COATING THE SAME WITH TIN. 